I wonder if you might advance him to kindergarten, and *IF* he exhibits signs of being behind at that level, then keep him in kdg again a second year.
we did 2x preK for my daughter that has a bday early october and she's so far advanced in kdg it's not funny, BUT, i would rather her be ahead than struggling. it makes school easy and fun instead of un-fun.
repeating at early ages is no big deal. if the cost thing is the problem, perhaps a year in kdg and if he struggles, then a second year in kdg which would be an easy year for him. it would correct the impression in his head that it's too hard/too challenging.
just a thought